Monitoring of steam quality during sterilization with improved temperature control

ABSTRACT

A device for detecting a non-condensable gas including a tube having an open end and a closed end, the tube and the closed end being closed with respect to a fluid, the open end open to allow the fluid to move into and out of the tube, and the tube configured to allow a condensed portion of the fluid to be removed from the tube by gravitation. The device includes a heat sink configured to extract heat from the tube at the closed end. The device further includes a heat source configured to supply heat to the open end of the tube and at least one thermometer configured to measure a temperature at a specific portion of the device or the fluid inside the tube.

FIELD OF THE INVENTION

The invention relates to monitoring of steam quality. The inventionfurther relates to monitoring of steam quality during sterilization. Theinvention further relates to a device and a method for detecting a gasin a fluid mixture. The invention in particular relates to detecting anon-condensable fluid in a gas mixture. The invention further relates toa device and a method to test and monitor steam quality during steamsterilization.

BACKGROUND OF THE INVENTION

Conditions for surface steam sterilization are predeterminedtime-temperature relations when saturated steam is present, e.g., 3minutes at 134° C. with saturated steam [MRC59]. These surface steamsterilization conditions are derived from sterilization of aqueousliquids, in which the mechanism for the killing of organisms iscoagulation of proteins [SYK67]. Sterilization is achieved if the liquidis kept at a certain elevated temperature for a sufficient amount oftime. In the literature several temperature-time combinations forsterilization have been documented. The results for aqueous liquids canbe used for surface steam sterilization [MRC59] if the steam heats upall surfaces to be sterilized to the required temperature and formscondensate on these surfaces. In the standard EN285 [EN285] this hasbeen translated to the requirement that steam should have direct contactwith the surfaces and the supplied steam may contain only a very smallamount of non-condensable gases (NCGs) (3.5 vol. %, relative to thecondensate, which corresponds to approximately 0.006 vol. % in the vaporphase). With NCGs in the steam gases are meant that will not condense inthe pressure and temperature range of steam sterilization. These rangesare generally 0 to 350 kPa and 0 to 150° C., respectively. The NCGs canbe introduced by or originate from the environmental air or dissolvedgases in the feed water for the steam generation. Examples of NCGsoriginating from the environment are a bad air removal before thesterilization phase, leaks in the sterilizer or the connected devices,such as a vacuum pump, and compressed air injected into the sterilizerby leaks in valves controlled by compressed air (typically 700 kPa) andgaskets.

Steam sterilizers can contain various components, e.g., mechanical,electronical and software components. These components can malfunctionunexpectedly. Also fluctuations in a steam supply can occur, forexample, fluctuations in the amount of NCGs in the feed water for steamgeneration. It is known that steam quality (the amount of NCGs presentin the steam) and the capacity for steam penetration of a sterilizervary over the day [VDO16-3]. The importance of ensuring a correct steamsterilization process is acknowledged in the standards for steamsterilization [EN285, EN13060, ISO17665], patents [U.S. Pat. No.5,270,217] and the literature [VDO13-2]. This demonstrates thatmonitoring is ‘good practice’ for steam sterilization processes.Moreover, according to these standards it is mandatory to monitor eachload, e.g., ISO 17665 clause 10.1 specifies: ‘Routine monitoring andcontrol shall be performed on each operating cycle.’ Currently,monitoring in steam sterilization is based on Biological, Chemical andPhysical indicators.

Clause 8.2.4 of the standard EN 285 [EN285] specifies an air detector.This device is based on a tube that is connected to the steam sterilizerchamber at one end whereas the other end, outside of the steamsterilizer, is closed. The temperature at the closed end of the tube ismeasured with a temperature sensor. This air detector has only limitedvalue, as already demonstrated in the note of clause 13.3.1 [EN285]:‘NOTE: This method does not necessarily express the true content of NCGin steam. The limiting value was defined experimentally in the 1960s inrelation to the sensitivity of air detectors commonly used in the UK atthat time. Repeated measurements give an idea of the true picture ofNCGs in the steam supply.’ Furthermore, because it qualifies conditionsbased on temperature measurements only, it cannot qualify steamconcentration or the presence of air (NCGs). Finally, it is a channelwith one end closed, of which the initial conditions are not specifiedand therefore not known. Therefore it is unclear what actually will bemeasured and where the energy for the observed temperature increase iscoming from.

Biological monitoring is performed with biological indicators (BIs).These indicators have the disadvantage that their integrity can only beguaranteed if the storage and handling is performed according to thespecifications given by the manufacturer. Apart from this, theincubation of the indicator will inevitably take time. Consequently,release of loads after sterilization will be delayed until the resultsof the indicators are available. Apart from this, their disadvantage isthat they only provide a one sided test. This implies that in case of aproblem, the information will often be insufficient for troubleshooting.

Chemical monitoring is performed with chemical indicators (CIs). Likethe BIs, also these indicators only provide a one-sided test. One of thedrawbacks of a CI is that it is rather inaccurate [VDO12-2] and many CIshave to be judged by subjective color interpretation [U.S. Pat. No.4,115,068]. Additionally, the CI can only be interpreted after thecomplete sterilization cycle has been performed and the CI is taken outof the load. Also the CI is often intended to mimic a biological killingmechanism. The correspondence of the relatively simple chemicalreactions with the complex biological killing mechanism is not obvious.

Currently, physical monitoring is known to be performed by monitoringpressure and temperature. From the pressure the so-called ‘theoreticaltemperature’ is calculated [EN285]. In the known method, the theoreticaltemperature is compared to the measured temperature. If the differenceis less than 2 K the steam is accepted as saturated steam. However,according to the literature [IAWPS] this assumption is not correct. Thecalculation of the theoretical temperature is based on thepressure-temperature relation for saturated steam and, consequently,only valid when saturated steam is present. Only measuring pressure andtemperature is not sufficient to ensure sterilization conditions[VDO14-1].

In some cases it is tried to measure if the steam injected into thesteam sterilizer chamber is saturated. If that is the case thepressure-temperature relation for saturated steam is used again.However, even if this method would be accurate enough, insufficientlyremoved initial air and leaks in the sterilizer chamber will not bedetected. Consequently, steam sterilization conditions cannot be ensuredby measuring the steam quality in the supply line of steam (outside ofthe sterilizer chamber), as is done by, e.g., the ‘SteamSpy’ from MMMGmbH, Germany [DE102010016017A1].

Over the years, a variety of physical instruments have been developedwith the aim to detect the presence of NCGs in the steam which ispresent in the sterilizer chamber. Many of these comprise a tube that islocated outside the sterilizer chamber, often connected to the drain ofthe sterilizer. This tube is closed at one end and designed such thatthe steam in the tube condenses and the NCGs are entrapped. The volumeof the entrapped NCGs is assumed to be a measure of the fraction of NCGspresent in the sterilizer chamber. In some cases the presence of NCGs inthe tube is deduced from temperature measurements [U.S. Pat. Nos.3,402,991, 3,479,131], in other cases the volume of the entrapped air ismeasured quantitatively, e.g., by measuring the water displacement [U.S.Pat. No. 3,967,494] or by optical means [EP0841069A2]. A fundamentallimitation of these methods is that the length of the tube used in theseinstruments is often so large, that the volume of the collected NCGssignificantly lags behind the concentration of NCGs present in thesterilizer chamber. Therefore these techniques are not suited to monitorthe steam quality in real time. Apart from this, it is not clear towhich extent these instruments yield quantitative information about thefraction of NCG's in the sterilizer chamber itself.

Finally, physical or electronic test systems that intend to measure thesteam quality within the sterilizer chamber are available in the market.It is reported that 3 out of 4 commercially available tests do notfulfil the claimed standard [BEN11]. DE202006006926U1 discloses a devicecalled EBI 15 (Ebro Electronic GmbH, Ingolstadt, Germany). EP1230936A1discloses a device called DPCD-3, Digital Process Challenge Deviceversion 3 professional (Interster International BV, Wormerveer, TheNetherlands). One device is based on the time derivative of thetemperature [VDO13-3]. This is the 3M™ Electronic Test System (ETS), 3MDeutschland GmbH, Neuss, Germany [WO201047139]. It is based on thedifference in heat transfer of steam and NCGs [VDO13-3]. This deviceshould only be used as a steam penetration test as specified in the ISO11140 part 4 [ISO11140-4]. This device is designed to use it only once aday. The results of the test are only available after the sterilizationprocess has finished, which makes the instrument unsuitable to monitorthe steam quality in real time. Finally, like all biological andchemical monitoring products mentioned so far, it requires manualhandling of human operators of sterilizers. This costs time in aproduction environment and has the risk of human errors. U.S. Pat. No.4,594,223 discloses heat sinks to identify NCGs.

Dutch Patent No. 2018932 discloses a device for detecting a gas,comprising a tube having an open end and a closed end, wherein the tubeand the closed end are closed with respect to a fluid, and the open endis open to allow the fluid to move into and out of the tube, and a heatsink configured to extract heat from the tube at the closed end of thetube. The device comprises at least one thermometer configured tomeasure a temperature at a specific portion of the device or the fluidinside the tube. The device may comprise a control unit configured toadjust a cooling power of the heat sink based on a temperature obtainedfrom the thermometer. The control unit can determine information about acomposition of the fluid inside the tube, in particular about a presenceof any non-condensable gas in the fluid, based on a temperature obtainedfrom the one or more thermometers or a cooling power related to the heatsink.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved device fordetecting a gas in a fluid mixture.

According to an aspect of the invention, a device for detecting a gas isprovided, comprising

a tube having an open end and a closed end, wherein the tube and theclosed end are closed with respect to a fluid, and the open end is opento allow the fluid to move into and out of the tube, wherein the tube isconfigured to allow a condensed portion of the fluid to be removed fromthe tube by gravitation;

a heat sink configured to extract heat from the tube at the closed endof the tube;

a heat source configured to heat a first portion of the tube up to aspecific temperature, wherein the heat source is located between theopen end of the tube and the heat sink; and

at least one thermometer configured to measure a temperature of a secondportion of the tube between the heat source and the closed end of thetube or the fluid inside that second portion of the tube.

The temperature of the wall of the tube is well-conditioned because thefirst portion of the tube is heated by the heat source. This way, thetemperature of the tube is less influenced by factors external to thetube, such as an object to which the tube may be connected, or thetemperature of the environment. The temperature profile of the tube inbetween the heat source and the heat sink may be largely determined bythe composition of the gas mixture at the open end of the tube. Thisway, the information obtained from the tube, such as a measuredtemperature, provides more accurate information about the presence of anon-condensable gas inside the tube.

The the heat source may be configured to keep the first portion of thetube at a constant temperature. This allows to set the temperature ofthe open end of the tube to a specific value, which is helpful tofurther avoid significant deviations of the temperature as a consequenceof external factors. By keeping the temperature of the open end of thetube constant, the climate (condensation, temperature profile, etc.)inside the tube is largely determined by the content of the gas mixturethat enters the tube through the open end of the tube.

The device may comprise a control unit configured to control the heatsource based on a temperature obtained from a thermometer configured tomeasure a temperature of the first portion of the tube. This allows tocontrol the temperature of the first portion accurately.

The control unit may also be configured to control the heat sink basedon a set-point for a temperature of the closed end of the tube. Thisallows to set the temperature of the closed end of the tube to aspecific value, which is helpful to avoid significant deviations of thetemperature caused by e.g. the content of the gas mixture flowing intothe tube. By keeping the temperature of the closed end of the tubeconstant, condensation of the condensable gases, such as water, may becontrolled better than by an unregulated heat sink.

The control unit may be configured to control the heat sink based on atemperature obtained from the at least one thermometer in respect of theclosed end of the tube. This way the heat sink may be controlled torealize e.g. a constant temperature or a well-defined temperature at theclosed end.

The tube may be enclosed by a thermally insulating layer. This makes thetemperature profile measurements less sensitive to variations ofenvironmental temperature.

The device may comprise a control unit configured to determineinformation about a composition of the fluid inside the tube, inparticular about a presence of any non-condensable gas in the fluid,based on a temperature obtained from the at least one thermometer or acooling power of the heat sink. Such a control unit may determine thecomposition efficiently.

The device may further comprise a container, wherein the open end of thetube is fluidly connected to an inside of the container via an openingin a wall of the container, and wherein the container is closable toform a substantially closable chamber that is fluidly connected to alumen of the tube. This way the device can be suitably used to detect anon-condensable gas inside the container.

The heat source may be configured to heat the open end of the tube to atemperature above a temperature of the inside of the container. Thisway, the measurement becomes more independent of the temperature of theinside of the container. Inadvertant condensation due to too cold inflowof gas may be avoided.

The chamber may be a sterilizer chamber. This allows to monitor thesterilization process by detecting any non-condensable gases in thesterilizer chamber.

The container may have the opening in a side wall or an upper wall ofthe container, wherein the chamber is fluidly connected to the inside ofthe tube via the opening. This allows to easily let the condensed fluidflow back into the chamber.

The tube may be fixed to the side wall or upper wall of the containerand the tube may protrude from the container in an upward direction.This allows to easily let the condensed fluid flow back into thechamber. Moreover, non-condensed fluids may remain in the tube, thusinfluencing the temperature profile inside the tube.

The heat source may be positioned outside the container. This way anyinfluence of the heat source to the sterilization process is avoided orreduced. Moreover, the temperature at the open end created by the heatsource is less influenced by the temperature of the wall of thecontainer. This way, the heat source may be used, for example, withoutactive temperature control. For example, the distance from the heatsource to a wall of the container, measured along the tube, may be atleast 2 centimeters, preferably at least 4 centimeters.

A distance between the heat sink (6) and the heat source (21) may be,for example, at least 5 centimeters, preferably at least 10 centimeters.This allows sufficient space for forming of a temperature profile insidethe tube related to a presence of non-condensable gases.

A distance between the heat source and the open end of the tube orbetween the heat source and the wall of the container, measured alongthe tube, may be, for example, at least 2 centimeters, preferably atleast 4 centimeters. A distance may help to make it easier to controlthe temperature of the portion of the tube at the heat source.

According to another aspect of the invention, a method of detecting anon-condensable gas in a gas mixture is provided. The method comprises

providing a gas mixture to a tube having an open end and a closed end,wherein the tube and the closed end are closed with respect to the gasmixture, and the open end is open to allow the gas mixture to move intoand out of the tube, wherein a condensed portion of the fluid is allowedto be removed from the tube by gravitation; and

extracting heat from the tube at the closed end of the tube using a heatsink;

heating a first portion of the tube up to a specific temperature using aheat source that is at a distance from the heat sink towards the openend of the tube; and

measuring a temperature of a second portion of the tube between the heatsource and the closed end of the tube or the fluid inside that secondportion of the tube, using at least one thermometer.

This method allows to detect non-condensable gases with a relativelyhigh accuracy.

The person skilled in the art will understand that the featuresdescribed above may be combined in any way deemed useful. Moreover,modifications and variations described in respect of the device maylikewise be applied to the method, and modifications and variationsdescribed in respect of the method may likewise be applied to thedevice.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed in more detail below, withreference to the drawings. Throughout the drawings, similar items may beindicated by means of the same reference numerals. It is noted that thedrawings are not on scale.

FIG. 1A shows a longitudinal cross section of a device to illustrate aprinciple of NCG detection using a tube in which condensation occurs.

FIG. 1B shows an axial cross section of the device shown in FIG. 1A.

FIG. 2A illustrates an example of a measurement probe using thetemperature distribution along the tube, which can be mounted to e.g.the upper wall of a sterilizer chamber.

FIG. 2B illustrates an example of a measurement probe using thetemperature distribution along the tube, which can be mounted to e.g. aside wall of a sterilizer chamber.

FIG. 3A illustrates an example of a measurement probe using the powerneeded to cool the closed end of the tube, which can be mounted to e.g.the upper wall of a sterilizer chamber.

FIG. 3B illustrates an example of a measurement probe using the powerneeded to cool the closed end of the tube, which can be mounted to e.g.a side wall of a sterilizer chamber.

FIG. 4 illustrates some examples of locations of the measurement probesat the wall of a sterilizer chamber.

FIG. 5 shows a flowchart illustrating a method of determining anon-condensable gas in a gas mixture.

FIG. 6 illustrates a method of detecting a non-condensable gas.

DETAILED DESCRIPTION OF EMBODIMENTS

Certain exemplary embodiments will be described in greater detail, withreference to the accompanying drawings.

The matters disclosed in the description, such as detailed constructionand elements, are provided to assist in a comprehensive understanding ofthe exemplary embodiments. Accordingly, it is apparent that theexemplary embodiments can be carried out without those specificallydefined matters. Also, well-known operations or structures are notdescribed in detail, since they would obscure the description withunnecessary detail.

One approach to assess steam quality is to measure parameters that arevery sensitive to the presence of small amounts of NCGs (generally air),such as the speed of condensation and the resulting heat transfer fromsteam to a surface.

An apparatus for measuring NCGs can comprise a hollow tube, closed atone end, comprising a thermally conductive wall, thermometers to measurethe temperature distribution along the tube in the axial direction, anda facility to control the temperature of the open end of the tube, forexample by heating the open end up to a certain temperature. Thetemperature distribution along the tube provides information about theamount of NCGs present in the sterilizer chamber. The apparatus canfurther comprise a facility to control the temperature of the closed endof the tube, for example by cooling the closed end, for example to atemperature that is lower than the heating temperature of the open end.

According to another aspect of the present disclosure, an apparatus formeasuring NCGs comprises a hollow tube, closed at one end, comprising athermally conductive wall, a thermometer to measure the temperature ofthe tube near the closed end of the tube, a facility to control thetemperature of the closed end of the tube, and a facility to control thetemperature of the open end of the tube, for example by heating the openend up to a certain temperature. The power needed to cool the closed endof the tube to a certain temperature that is lower than the heatingtemperature of the open end provides information about the amount ofNCGs present in the sterilizer chamber.

According to an aspect of the present disclosure, the apparatus maycomprise a steam sterilizer comprising a sterilizer chamber, wherein thesteam sterilizer is configured to inject steam into the sterilizerchamber to sterilize an object within the sterilizer chamber; whereinthe open end of the tube has a fluid connection to the sterilizerchamber. The fluid connection of the tube to the sterilizer chamberallows assessing the steam conditions inside the sterilizer chamber. Thesteam sterilizer may further be configured to evacuate the sterilizerchamber before injecting the steam or to perform evacuation ofsterilizer chamber and injection of the steam alternatingly.

According to another aspect of the present disclosure, the steamsterilizer may be configured to repeat the steps of evacuation andinjection until the amount of NCGs detected by the apparatus satisfies acertain predetermined constraint.

The measurement tube may be connected to any wall of the sterilizerchamber but preferably not to the bottom wall. However, it is stillpossible to connect the tube to the bottom of a container such as asterilizer chamber. In such a case, preferably a way to drain condensedliquid out of the tube is provided.

The apparatus may comprise a control unit configured to, preferablyrepeatedly during a sterilization process performed by the steamsterilizer, receive the temperature distribution along the tube and/orthe power needed to cool the closed end of the tube.

This is helpful to assess during what time period or which time periodsthe sterilization conditions are met. For example, sterilizationstandards may prescribe a certain period of time during which saturatedsteam should be present at the surfaces that have to be sterilized. Byanalyzing the temperature distribution and/or the cooling powerrepeatedly during an interval, it can be assessed whether the prescribedperiod has been reached.

The steam sterilizer may be configured to adjust the sterilizationprocess based on analysis of the temperature distribution along the tubeand/or the power applied to cool the closed end of the tube. Forexample, if sufficient cooling power is needed at a given time period t,then the steam sterilizer may be configured to continue itssterilization process for at least a predetermined time interval Δt, upto t+Δt. Also, if too little cooling power is needed at a time at whichsaturated steam was expected to be present, the sterilizer may beconfigured to adjust the process for example by increasing the supply ofsteam. Other manners of adjusting the process based on the observedtemperature distribution and/or cooling power may also be applied.

A device for detecting a non-condensable gas, as described above, may beimplemented in various ways, of which an example is illustrated inFIG. 1. The illustrative device comprises a vertically oriented tube 1with an open bottom end 5, which can be fluidly connected to thesterilizer chamber or another kind of space, whereas the other end 12 isclosed. A heat source 21 is arranged near the open end 5 of the tube 1.A heat sink 6 is arranged near the closed end 12 of the tube 1. The heatsource 21 is configured to heat the open end of the tube to atemperature above the condensation temperature of the condensable gas,whereas the heat sink 6 is configured to cool the closed end of the tubeto a temperature below the condensation temperature of the condensablegas.

The heat source 21 may comprise an electric heater, for example.Alternatively, the heat source 21 may be implemented by flushing a hotfluid along the wall of the tube, for example steam tapped from thesteam generator of the sterilizer. Other implementations of the heatsource may be apparent to the person skilled in the art on the basis ofthe present disclosure. The heat source 21 may be controlled by acontrol unit to realize a predetermined temperature at the open end 5 ofthe tube 1.

When in use, a mixture of steam and air 2 may enter the lumen 19 of thetube 1. As long as the wall of at least a portion of the tube has alower temperature than the saturation temperature of the condensable gasin the gas mixture entering the tube, the steam will condense on thewall of the tube. The condensate 4 runs off the wall towards the bottomof the tube, where it leaves the tube through the open end 5. If thewall of at least a portion of the tube is kept at a temperature belowthe saturation temperature of the steam, this condensation willestablish a continuous flow of steam (and possible non-condensable gas)into the tube during the process until the end of the sterilizationphase. Non-condensable gas flowing with the steam into the tube will notcondense and can only leave the tube 1 via the open end 5 of the tube bydiffusion. However, diffusion is a very slow process compared to theflow initiated by the condensing steam on the wall. Therefore, in thetube, the non-condensable gas will accumulate and the concentration ofthe condensable gas will substantially decrease. This effect will bemore pronounced towards the closed end 12 of the tube, where so muchnon-condensable gas 3 can be present that the condensable gas may not beable to penetrate all the way up to the closed end 12.

The heat transfer from the gas mixture to the wall of the tube isdominated by the latent heat that is released during condensation of thesteam. The presence of even small amounts of non-condensable gas willsignificantly reduce this heat transfer. Therefore, it is expected thatthe heat load on the tube close to the closed end 12 is smaller than theheat load on the tube close to the open end 5. This difference in heatload will be more pronounced when the fraction of non-condensable gas ofthe gas inflow is larger. More particularly, when more non-condensablegas has accumulated near the closed end of the tube, a larger portion ofthe tube near the closed end of the tube will be exposed to reduced heatload and thus will attain a lower temperature, and thus the temperatureprofile along the tube depends on the fraction of non-condensable gas inthe gas mixture that flows into the tube, as the condensed gas (i.e.liquid) exits the tube.

In the following, exemplary aspects of a device to analyze steam will bedescribed in greater detail. However, it will be understood that thedetails disclosed herein are merely intended as illustrative examples.In certain implementations, the tube 1 is made of a material that hasgood heat conduction properties. Also, the heat conduction in axialdirection may be good. For example, the heat conductivity of the tubematerial may be isotropic. The open end 5 of the tube may be connectedto a side wall or upper wall of a sterilizer chamber, such that itsentrance has a fluid connection to the sterilizer chamber 401. Theclosed end 12 of the tube may be kept at a constant temperature by acooling facility 6. This cooling facility 6 may comprise a heat sink,cooled by environmental air, and/or a cooling liquid, but may also beimplemented by other means, for instance, by using a Peltier cooler. Theopen end 5 of the tube may be kept at a constant temperature by aheating facility 21. The heating facility 21 may comprise a heat source,heated by a heating liquid, but may also be implemented by other means,for instance, by using an electric resistance. The complete tube 1 maybe thermally isolated from its environment, except at the coolingfacility 6, at the heating facility 21, and at the open end 5 of thetube 1.

The cooling of the closed end 12 of the tube 1, in combination with theheat conduction of the tube 1 in the axial direction 13, favors a walltemperature which is below the saturation temperature of the steamcomprised in the steam-air mixture entering the lumen of the tube 1through the open end 5 of the tube 1. The resulting dynamics of themixture of steam and non-condensable gases inside the lumen has alreadybeen outlined above. Using thermodynamic calculations, it can be shownthat in the above-described configuration, the temperature distributionalong the axial direction of the tube is directly related to thefraction of non-condensable gases that is present in the mixture ofsteam and non-condensable gases at the entrance of the tube. Backgroundinformation regarding thermodynamic computations has been reported inthe literature [VDO13-3].

It is observed that in the application domain of, for example,sterilization, a condensable gas is used for sterilization purposes.This condensable gas may be water vapor or steam. Moreover, such acondensable gas may be contaminated with one or more non-condensablegases. These one or more non-condensable gases are usually dominated bythe non-condensable gases that are present in environmental air.However, steam and air are only examples of condensable andnon-condensable gases, respectively. Throughout this description of adevice and method of detecting a non-condensable gas, the word steam maybe replaced by any condensable gas, and the word air may be replaced byany non-condensable gas.

If the diameter of the tube is much smaller than its length, for exampleif the diameter of the tube is at least about a factor 10 smaller thanits length, the transport of the steam-air mixture within the lumen 14of the tube 1 can be described fairly accurately by a one-dimensionalmodel. In such a model, the equation for the conservation of mass of amixture component i (which may be, for example, steam or air) may begiven by:

${\frac{\partial\rho_{i}}{\partial t} + \frac{{\partial\rho_{i}}\overset{¯}{u}}{\partial t}} = {{\frac{\partial}{\partial z}\left( {\rho D*\frac{\partial\left( {\rho_{i}/\rho} \right)}{\partial z}} \right)}.}$

Herein, t is the time, ρ_(i) the density of component i, ρ the totaldensity of the mixture, ū the local velocity of the mixture averagedover the tube inner cross section, and z the (axial) position along thetube. D* is a modified diffusion constant, which appears because of theradial dependence of the velocity (Taylor dispersion). The boundaryconditions at the open end 5 of the tube (z=0) are determined by thesteam-air mixture in the sterilizer chamber and the heat source.

The heat transfer from the steam-air mixture to the wall of the tube isdominated by the condensation of water vapor. This heat transfer can bedescribed by standard Nusselt boundary layer theory. In very goodapproximation, the local heat transfer per meter (q_(m)) from saturatedsteam to the wall of the tube is given by:

q_(m)(z) = P_(m)(z){T_(sat)(z) − T_(w)(z)}^(3/4)(z − L_(tube))^(−1/4).

Here T_(sat) is the saturation temperature of the steam, T_(w) the walltemperature, L_(tube) the tube length and P_(m) a parameter withdimension W/m which depends on several physical properties of water andsteam and the tube diameter. If non-condensable gases, such as air, arepresent, the heat transfer to the wall is significantly lower. This canbe accounted for by making P_(m) a function of the air fraction. Moredetails about this heat transfer can be found in the literature[VDO13-3].

If the outer side of the tube is thermally isolated from itsenvironment, the temperature T_(w) of the wall can be described by:

$\frac{\partial T_{w}}{\partial t} = {{\frac{k_{w,z}A_{w,z}}{C_{w}}\frac{\partial^{2}T_{w}}{\partial^{2}z}} + {q_{m}.}}$

Herein, k_(w,z) denotes the heat conductivity of the tube wall in theaxial direction 13 and A_(w,z) denotes the cross-sectional area of thetube wall 15 perpendicular to the axial direction. C_(w) represents theheat capacity of the tube wall 15 per meter in axial direction and q_(m)denotes the heat transfer from the gas mixture to the tube wall bycondensation.

Numerical solutions, for example, of the resulting set of three coupledsecond order partial differential equations may show the behavior thatwas qualitatively outlined above. When no gas mixture or only air ispresent in the sterilizer chamber and in the tube 1, the temperature ofthe wall of the tube 1 may drop linearly from the temperature of theheat source 21 close to the open end of the tube 1 to the temperature ofthe heat sink 6 at the closed end 12 of the tube. At very low fractionsof air in the sterilizer chamber, the steam penetrates almost towardsthe closed end 12 of the tube. In this case the temperature of the partof the tube wall towards the heat source is almost equal to that ofsaturated steam, except close to the heat source, where the temperatureis slightly higher, whereas the temperature of the tube wall drops tothat of the heat sink near the closed end 12 of the tube 1. As thefraction of air in the sterilizer chamber increases, more airaccumulates near the closed end 12 of the tube 1, and the temperaturedrop along the tube wall occurs at larger distance from the closed end12, closer to the open end 5. Therefore, the temperature profile alongthe tube 1 in the axial direction 13 provides information about thefraction of air that is present in the sterilizer chamber 401. Thenumerical computations also reveal that the temperature distributionalong the tube responds to changes in the air fraction within thesterilizer chamber rather quickly. For example, for a tube with a lengthof 15 cm, equilibrium may be established within a few seconds for smallair fractions, increasing up to a few minutes for air fractions whichare so large that they would preclude proper sterilization conditionswithin the sterilizer chamber. This implies that the device disclosedherein can provide information about the fraction of air within thesterilizer chamber at time scales that are generally much smaller thanthe time scale of a typical sterilization process. This is a largeadvantage compared to other instruments, such as the ETS, which have amore or less integrating behavior and/or yield results only after thecomplete sterilization process has finished.

FIG. 2A shows an example of a possible realization of a measurementdevice. The realization according to FIG. 2A is implemented using astraight tube. For example, the measurement device can be mountedvertically on the upper wall of a sterilizer chamber. The open end 5 maybe fluidly connected to the interior of the sterilizer chamber. However,the device can be applied differently, to measure steam and gasproperties in any kind of application besides sterilizer chambers.

FIG. 2B shows another example of a measurement device. The realizationshown in FIG. 2B may be mounted, for instance, on a side wall of thesterilizer chamber, in such a way that the tube has a substantiallyvertically oriented portion 16 and a substantially horizontally orientedportion 17. However, this is not a limitation. In some otherembodiments, the tube may be diagonally oriented, or curved, forexample. In certain embodiments, the tube 1 is fixed to the sterilizerchamber in such a way that the condensed liquid on the inner wall of thetube 1 flows back towards the opening 5 and flows back out of the tube 1back into e.g. the sterilizer chamber by gravity. In both realizationsof FIG. 2A and FIG. 2B, the tube 1 may be connected to a flange 9 thatallows the device to be easily connected to e.g. a sterilizer, but manyalternative means to connect the device are possible instead of theflange 9. On the heat sink 6 a thermometer 7 may be attached that may beused to read and/or control the temperature of the heat sink 6.

A heat source 21 is connected to the tube closer to the open endcompared to the heat sink 6. In certain implementations, a thermometer22 is attached to the tube close to the heat source 21. This thermometer22 can be used to control the heat source 21 or to detect a boundarycondition for the above-described physical model. In certainimplementations the thermometer 22 may be a component of the heat source21.

Along the tube 1, one or more thermometers 8 may be attached. Thesethermometers may serve to monitor the temperature profile in the axialdirection 13 along the tube. In the device shown in FIG. 2A, thethermometers 8 are attached to the tube with equal spacing; in thedevice shown in FIG. 2B the spacing between adjacent thermometersbecomes gradually smaller towards the closed end of the tube. The latterimplementation may enhance the resolution of the instrument in case ofrelatively small air fractions in the sterilizer chamber, because forthese fractions the steam penetrates further into the tube. The numberof thermometers included in the figures and their spacing are only shownby means of example; many other configurations are possible. Forexample, the equal spacing shown in FIG. 2A may be applied to the curvedtube shown in FIG. 2B, and the unequal spacing of the thermometers asshown in FIG. 2B may be applied to the straight tube shown in FIG. 2A.Moreover, measurements with a single thermometer may already providesufficient information to detect the presence of a non-condensable gas.

When the temperature drop occurs near the closed end of the tube, thedistance from the place of the temperature drop to the heat sink issmall. This implies that a relatively large cooling power is deliveredby the heat sink to the tube in order to keep the closed end of the tubeat a chosen temperature. If the temperature drop occurs at a largerdistance from the heat sink, the cooling power is significantly smaller.Therefore, the cooling power needed to keep the heat sink or the closedend of the tube at a chosen temperature or, alternatively, the coolingpower delivered by the heat sink to the tube, is directly related to theposition of the temperature drop along the tube and, consequently, tothe fraction of non-condensable gas, such as air, in the sterilizerchamber. Thus, the control unit may be configured to detect the presenceof non-condensable gases based on the cooling power needed to keep theclosed end of the tube or the heat sink at the chosen temperature.

An example of a realization of a measurement device based on thisprinciple is shown in FIG. 3A and FIG. 3B. In the examples of FIG. 3Aand FIG. 3B the thermometers 8 along the tube 1 have been omitted, eventhough thermometers may be provided along the tube as desired. A thermalresistance 11 has been included between the heat sink 6 and the closedend 12 of the tube 1. One thermometer 7 may be attached to the heatsink, to monitor and/or control the temperature of the heat sink 6. Twothermometers 10 may be attached to the thermal resistance 11 between theheat sink 6 and the closed end 12 of the tube 1. Of the two thermometers10, a first thermometer 10 a is fixed closer to the heat sink 6 than asecond thermometer 10 b, and the second thermometer 10 b is fixed closerto the closed end 12 of the tube 1 than the first thermometer 10 a.Advantageously, the second thermometer 10 b is used as a feedbacktemperature to control the heat sink 6. That way the closed end of thetube may be controlled relatively accurately.

At least two different ways are possible to determine the power consumedto cool the closed end 12 of the tube 1 to a chosen temperature. First,the power can be deduced from the externally supplied cooling power(either thermal or electric), while keeping the temperature measuredwith the thermometer 10 b at the chosen temperature. Second, thiscooling power can alternatively be deduced from the temperaturedifference between the two thermometers 10 a, 10 b attached to thethermal resistance 11. In the latter case variations of the observedcooling power due to changes in the environmental temperature may bestrongly suppressed, which may improve the accuracy of the measurementof the NCG fraction. It should be noted that if the cooling power isdeduced from the externally supplied cooling power, only one of thethermometers illustrated at 7 and 10 a, 10 b (or even 8) are needed, andthe remaining illustrated thermometers can be omitted. It should benoted that the realizations depicted in FIG. 3 are only examples; alsocombinations of the features depicted in FIG. 2 and FIG. 3 are possible.

FIG. 3A and FIG. 3B differ in the shape of the tube. These differencescan be combined in any way as explained above with reference to FIG. 2Aand FIG. 2B. As shown in FIG. 2B and FIG. 3B, the location of the heatsource 21 may be chosen closer to or further away from the open end 5 ofthe tube 1. Moreover, the heat source 21 may be attached to a verticalportion 16 of the tube, to a horizontal portion 17 of the tube, asillustrated, or to a diagonal portion of the tube.

In a specific, more detailed, example of a possible realization of thedevice according to FIG. 2A and FIG. 2B the tube 1 may have a length ofabout 15 cm, an inner diameter (=lumen diameter) of about 6 mm, and anouter diameter of about 10 mm (thus, a thickness of the tube wall ofabout 2 mm). The tube may be made of, for example, a metal, such asstainless steel. For example, stainless steel grade 316L may be used.The open end 5 may be fitted with a flange 9, for example a Triclampflange, to enable easy fixation to the sterilizer chamber. The flange 9may be fitted to the sterilizer chamber in such a way that the lumen ofthe tube is in fluid communication with the inside of the sterilizerchamber via the open end 5 of the tube 1 and a hole in the wall of thesterilizer chamber. The thermometers 7, 8, 10, 22 may comprisethermocouples, for example, type K thermocouples, or Pt resistancethermometers, for example Pt100 or Pt1000. In such a configuration theheat conduction in the axial direction 13 of the tube may be about 10⁻³Wm/K. The heat sink 6 may be controlled to maintain a temperature ofabout 45° C. The heat source 21 may be controlled to maintain atemperature of about 138° C. However, these numerical values are onlyprovided as illustrative examples.

The dimensions and materials of the tube can be chosen with a greatvariability. As a practical example, a length measured along a centralaxis of the tube (1) from the open end (5) to the closed end (12) can bebetween 10 cm and 30 cm. A diameter of a cross section of the lumen ofthe tube (1) can be between 3 mm and 20 mm. Also, a thickness of thewall (15) of the tube (1) can be between 1 mm and 5 mm. As to thematerial, as examples, the tube may be made of thermally conductivematerials such as a metal such as Cu, Al, Cr, Fe, or Ni, or any alloycontaining any two or more of these elements. Alternatively, the tubemay be made of a polymer. In any of the disclosed embodiments, the tubemay be covered by a thermally isolating material. Also, in any of thedisclosed embodiments, the heat sink at the closed end of the tube maybe the only heat sink of the measurement device. That is, in certainembodiments, no further heat sinks are present along the tube except forthe heat sink 6. Moreover, in certain embodiments, no further heatsources are present along the tube except for the heat source 21. Incertain embodiments, during detection of non-condensable gases, nofurther active heat sinks are activated except for the heat sink at theclosed end of the tube. In certain embodiments, during detection ofnon-condensable gases, no further active heat sources are activatedexcept for the heat source at the open end of the tube.

Condensation properties of a gas depend on the temperature and pressurethat is applied to the gas. Accordingly, where in this disclosure“non-condensable gas” is mentioned, this may be understood to be a gasthat does not condense at the applied temperature and pressure, i.e., anon-condensing gas.

During the sterilization phase of a sterilization process, thetemperature profile along the tube may decrease almost linearly from thesterilization temperature (for instance, 134° C.) at a location close tothe heat source at the open end of the tube to the maintainedtemperature of the heat sink (for instance, 45° C.) at the closed end,when large fractions of air (for example, about 1%) are present in thesterilizer chamber. In such a situation, the power needed to cool theheat sink may be of the order of about 0.5 W, for example. For smallerair fractions (0.05%) during the sterilization phase, the temperature ofthe tube at 5 cm away from the closed end 12 may be as high as 134° C.,and may decrease from 134° C. at 5 cm from the closed end of the tube to45° C. at the closed end. In that case, the power needed to cool theheat sink may be larger, for example of the order of about 2 W. For verysmall air fractions (0.005%), the temperature may decrease from 134° C.at 2 cm from the closed end of the tube to 45° C. at the closed endduring the sterilization phase. In that case, the power needed to coolthe heat sink may be of the order of about 5 W. These numbers depend onthe actual configuration (materials, dimensions, etc.) of the device. Toreduce the cooling power, in certain implementations, the cooling powermay be maximized to a certain maximum cooling power, e.g. 2 W, when thetemperature is above the temperature-to-be-maintained but below themaximum temperature at which a sufficient amount of the condensable gascondenses given the existing parameters such as pressure. Such aconfiguration would allow e.g. to detect a non-condensable gas when lessthan the maximum cooling power is needed.

In a particular example, the highest temperature achieved by asterilizer may be 134 degrees Celsius. The temperature of the open endof the tube regulated by the heat source may then preferably chosen asclose as possible to this highest temperature of 134 degrees Celsius, orpreferably even higher. If the temperature of the sterilizer at thelocation of the measurement device does not usually become as high as134 degrees Celsius, a slightly lower temperature at the heat source maybe sufficient. This applies also to sterilizer temperatures differentfrom 134 degrees Celsius. In general the heat source may be configuredto heat a portion of the tube up to the sterilization temperature used,or higher.

A calibration procedure and/or numerical solutions of the equationsdisclosed above may be used to relate the temperature readings of thethermometers and/or the cooling power needed to keep the heat sink orthe closed end of the tube at the chosen temperature to the air (NCG)fraction in the sterilizer chamber. For example, a list of possiblemeasurement values and their corresponding NCG fraction may be stored ina look-up table.

FIG. 4 shows a schematic representation of a sterilizer apparatus. Onlyfeatures relevant to an understanding of the present disclosure havebeen illustrated in FIG. 4. Features not necessary for an understandingof the measurement device have been omitted. The sterilizer apparatuscomprises walls 402 forming an at least substantially closablesterilizer chamber 401. The sterilizer chamber 401 may have a loadablespace 405, in which load 406 may be put. For example, at least one ofthe walls 402 may comprise a closable opening for inserting and removingthe load 406 into and out of the sterilizer chamber 401. This load 406may comprise for example a pack of textile and/or one or more medicaldevices to be sterilized. Such medical devices may include heavyinstruments and/or tubular instruments such as catheters, which warm upvery slowly if substantial fractions of NCGs are present within thesterilizer chamber.

The sterilizer chamber 401 may be fluidly connected to a pump 403. Whenthe sterilizer chamber 401 is closed, the pump 403 may be optionally beconfigured to perform a pumping operation to remove any fluid from thesterilizer chamber 401 to create a vacuum inside the sterilizer chamber401. The sterilizer may also comprise a steam generator 404 including awater supply and facilities to vaporize and heat the water. The steammay be conditioned, so that steam that is injected into the sterilizerchamber 401 may have predetermined properties including for example apredetermined temperature and/or a predetermined humidity. The steamgenerator 404 may comprise an electrical or other type of heat source toheat and vaporize the water. Alternatively, the steam may be suppliedfrom an external source, such as a central steam generator of ahospital.

A typical sterilization process comprises three phases. The first phaseis the conditioning phase, during which the air that is initiallypresent in the sterilizer chamber is removed and the load is heated upto the sterilization temperature. This is generally achieved bysuccessive cycles of evacuating the chamber by the pump 401 andinjecting saturated steam from the steam generator 404. The second phaseis the actual sterilization phase, during which the sterilizer chamberis filled with saturated steam and kept at the specified temperature(generally by controlling the pressure) for a specified time. During thethird phase the sterilizer chamber is evacuated to dry the load andfinally filled with air to atmospheric pressure to return to a safestate where it can be opened. Notwithstanding the above-disclosedtypical sterilization process, alternative processes may be used toachieve the steam sterilization. The measurement devices disclosedherein may be used in conjunction with any suitable sterilizationprocess.

One or more measurement devices disclosed herein can be used to monitorthe sterilizing conditions inside the sterilizer chamber 401. However,the measurement devices disclosed herein may also be used in othermeasurement applications. Moreover, the measurement devices disclosedherein are not limited to being used in conjunction with a sterilizer orsterilization procedures. Rather, they can be used to measure steamquality properties of any gas mixture, in particular steam. In anexemplary implementation, the gas mixture is in a container, and thedevice (in particular the open end of the tube) is in fluidcommunication with the gas mixture inside the container.

FIG. 4 illustrates two examples of how a measurement device according tothe present disclosure may be arranged with respect to the sterilizerchamber 401. However, these arrangements are only disclosed by means ofexamples, without limiting the present disclosure thereto. As discussedabove, the sterilizer chamber 401 could be replaced with any kind ofcontainer. The application of the measurement device to any kind ofcontainer may be realized in a similar way.

In the first example, the measurement device 410 is fitted to the upperwall 450 of the sterilizer chamber 401 such that the lumen of the tube411 has a fluid connection to the interior of the sterilizer chamber402. The tube 411 of the device 410 is thermally insulated from theenvironment by an insulating material 407. In this way, heat transportin the radial direction from the tube 411 of the device 410 to theenvironment is greatly reduced. A part of the heat sink 416 may be inthermal contact with the environment, either directly or indirectly, totransport heat away from the tube 411 towards the environment. A heatsource 422 is provided near the open end of the tube.

In the second example, the measurement device 420 is connected to a sidewall 451 of the sterilizer chamber 401. The setup including tube 421,thermally insulating material 409, heat sink 426, and heat source 423 isotherwise similar to that outlined for the first example.

To promote that the condensed steam exits the tube by gravity andreturns into the sterilizer chamber, the tube 411 of the measurementdevice 410 is a straight tube extending in vertical direction from theupper wall 450. Likewise, the tube 421 of the measurement device 420extends from the side wall 451 of the sterilizer and tends in an upwarddirection.

In a practical implementation, typically either one of the devices 410and 420 will be provided, and the other one omitted. However, this isnot a limitation. It is also possible to provide more than onemeasurement device to provide multiple measurements of the samecontainer.

In any of the above arrangements, the thermometers may be read out by adata-acquisition system, for example the control unit 430, whichprocesses and analyzes the temperature measurements, for example thetemperature profile in the axial direction of the tube, and/or thecooling power applied to keep the heat sink or the closed end of thetube at the chosen temperature. This analysis may, for example, yieldthe fraction of air that is present in the steam-air mixture in thesterilizer chamber 401. The analysis may involve looking up the detectedtemperature(s) and/or cooling power in a look-up table and retrievingthe fraction of air from the look-up table. The look-up table may begenerated by suitable experiments and/or may be computed based on theabove-disclosed equations.

The results of this analysis may be used, for example, to generate analarm signal if the fraction of NCGs during the sterilization phase isabove a predetermined threshold. On the other hand, the results can(also) be sent to a control unit 430, which may be configured to controlthe operation of the sterilizer chamber 401 including injection of steamby the steam generator 404 and removal of fluid from the sterilizerchamber by the pump 403. Also, the control unit 430 may be configured toreceive the measurement signals and/or measurement data generated by thedevice 410 and/or the device 420. The control unit 430 may be configuredto control the heat source 422, 423 and/or the heat sink 416, 426, basedon the received temperature measurements and optional power consumptionof these components. The control unit 430 may be configured to controlthe power applied by the heat source and/or heat sink so that atemperature at the respective component is kept as close as possible to(or within a certain range around) a certain predetermined temperature.This is referred to herein as keeping a constant temperature.

The control unit 430 may be configured to generate an alarm signal ifthe fraction of NCGs is determined to be above a predeterminedthreshold. The control unit 430 may also be configured to adaptdynamically, for instance, the timing of the sterilization process basedon the measurement result and/or the alarm signal.

The control unit 430 may be configured to provide real-time informationabout the measured values and/or computed values. Also, the control unit430 may be configured to detect the steam quality (the fraction of NCGs)during every sterilizing process.

Also, the control unit 430 may be configured to deliver at least some ofthe detected and/or computed results to an external system (notillustrated), such as a hospital ‘track and trace’ information system.In such a system, the digital information may be coupled to specificpatient files. Also, the digital information can be coupled to arelevant instrument. This relevant instrument can be the sterilizerdevice. Alternatively, digital information can be coupled to the devicethat was sterilized. Also, the digital information can be coupled to amaintenance system associated with the sterilizer device. For example,if malfunctioning is detected, the system can send a signal to amaintenance service, so that service may be provided to repair thesterilizer device. Additionally, the information of the sterilizationprocess used for medical devices can be coupled to patient files inorder to improve patient safety.

The devices and methods disclosed herein allow monitoring variables thatare relevant for determining steam sterilization conditions. They allowmonitoring steam quality for every load of the sterilizer. The devicecan provide the measurement information in real-time. Also, it can beused to obtain more insight in the steam sterilization processes.

The system offers the possibility to monitor directly whethersterilization conditions are satisfied or not. The data of themeasurements can be made available in real-time, so they can be used forprocess control or process optimization.

In an alternative implementation, the tube 1 of the device may be fixedor positioned loosely inside a space or container containing the fluidto be analyzed. Insulation material around the tube may be provided tostill be able to create the temperature conditions as describedhereinabove. If the heat sink 6 is a passive heat sink, such as athermal capacitor, which may be made from aluminum, the insulatingmaterial may be provided around the heat sink as well. If the heat sink6 comprises an active cooling element, for example a Peltier element,the insulation material may be omitted at a heat source of the coolingelement, so that heat can be actively removed from the tube 1. The heatsource of the cooling element may be attached to an opening in the wallof the container, so that the cooling element can operate moreefficiently.

By appropriately tuning the temperatures, including the targettemperature of the heat sink and the look-up tables correlatingmeasurements with information regarding NCGs, the device can be used todetect non-condensable fluids in other gases.

In the above, an improved detector of a non-condensable gas has beendescribed. In certain implementations thereof, the tube comprises afirst section 201, extending from the open end of the tube or the wallof the container, to which the open end of the tube may be connected, upto and including the heat source. The tube further comprises a secondsection 202, extending in between the heating element and the closed endof the tube. This second section 202 may be considered the measurementsection. The dimensions (i.e. inner diameter, wall thickness, length) ofthe second section 202 are related to the described physical model ofthe temperature profile. The dimensions of the second section 202 mayinfluence the sensitivity for non-condensable gases and response time.Examples of these dimensions are disclosed in the present disclosure.

In case of applying the measurement device to a sterilizer, the heatsource may be controlled to provide a target temperature of at least alittle above the sterilization temperature. In general, this targettemperature may be set to a value above the temperature of the gasmixture in the container, or in absence of a container, the temperatureof the environment of the tube. The heating element may thus preventuncontrolled condensation of the inflowing gas mixture in the firstsection 201. In case the sterilization temperature or the temperaturecaused by e.g. a process in the container can vary within a prescribedtemperature range, for example +/−two degrees Celsius, the targettemperature may be set, for example, to a temperature above the upperlimit of the temperature range.

The dimensions of the first section 201 can be chosen with much freedom.Preferably the inner diameter of the first section 201 is at least aslarge, or larger, than the inner diameter of the second section. If theinner diameter of the first section 201 is larger, this may reduce anyadverse effects of any condensation in the first section 201. Suchcondensation could possibly occur in between the open end 5 and the heatsource 21, for example if the temperature of the wall of the containeris temporarily below the condensation temperature of the gas mixture inthe container.

The inner diameter of the tube does not have to be the same through thewhole tube. For example, the first section 201 may be wider than thesecond section 202. In another example, the inner diameter of the secondsection 202 could be smaller towards the closed end 12 (tapered).

By keeping the first section 201 short, the response time of thedetector may be kept relatively short. In certain embodiments, bykeeping a certain distance between the heat source 21 and the wall 450of the container, the portion of the tube at the heat source 21 can beheated more reliably.

FIG. 5 illustrates a method of determining a non-condensable gas in agas mixture. In step 501, a device with a tube having a closed end witha heat sink and an open end is provided, as outlined hereinabove. Aspart of step 501 the open end of the tube may be fluidly connected tothe sterilizer chamber. In step 502, heat is extracted from the tube atthe closed end of the tube using the heat sink. This step may comprisecontrolling to provide electric power to the heat sink, which maycomprise an active component such as a Peltier element. Alternatively,step 502 may comprise pre-cooling a passive cooling element. In step 502a, a portion of the tube at the open end of the tube is heated using aheating element. The portion may be kept at a predetermined temperature.In step 503, steam or another gas or a gas mixture is provided to theopen end of the tube. This step may be part of a steam sterilizationprocedure, as outlined hereinabove. Sterilization procedures are knownin the art per se.

In step 504, it is decided whether to perform a temperature measurement.In certain implementations the temperature measurement is performedcontinuously, in other implementations this may be performed at certaintime points defined by an application program, for example. In step 505,if the temperature measurement is to be performed, the temperaturemeasurement is performed at one or more points of the device. This stepmay comprise receiving a signal from the corresponding thermometer orthermometers, converting the signal to a digital value, and storing thedigital value in a memory.

In step 505 a, it is decided whether to perform control of the heatingpower of the heat source. This may depend on the implementation. Forexample, in case a source of heat (e.g. a fluid) with an appropriatetemperature and sufficient power is available to provide heat to theportion of the tube, it may be appropriate to skip the control of theheat source and proceed to step 506. In step 505 b, in case the heatingpower is to be controlled, the heating power of the heat source iscontrolled based on the measured temperature at the portion of the tubeclose to the heat source. For example, if the measured temperature isbelow a lower threshold, the heating power may be increased. On theother hand, if the measured temperature is above an upper threshold, theheating power may be decreased or the heat source may be switched off.

In step 506, it is decided whether to perform control of the coolingpower. This may depend on the implementation (passive or active heatsink). Also, the cooling power may be adjusted at certain timeintervals, which may be monitored using a timer in step 506. In step507, if the cooling power is to be controlled, the cooling power of theheat sink is controlled based on the measured temperature. For example,if the measured temperature at a specific one of the thermometers isbelow a lower threshold, the cooling power may be reduced. On the otherhand, if the measured temperature at the specific thermometer is abovean upper threshold, the cooling power may be increased. The specificthermometer may be a thermometer at the heat sink (see 7), at a thermalresistance (see 10 a, 10 b), or a thermometer on the tube itself (see8). In the latter case, preferably a thermometer close to the closed endof the tube is used for this purpose.

Finally, in step 508, the presence of a non-condensable gas may bedetected. For example, the measured temperatures and/or the powersupplied to the heat sink is combined and converted to a concentrationof non-condensable gas using an equation or a look-up table.Alternatively, the power used by the heat sink or the power transferredto the closed end of the tube to realize a particular temperature may beused as an input. Alternatively, the condensation occurring in the tubemay be observed visually (e.g., using a transparent tube or a camera),or using a capacitive detection method. Condensation happening closer tothe closed end of the tube indicates a smaller concentration ofnon-condensable gas.

FIG. 6 illustrates a method of detecting a non-condensable gas. In step601, a gas mixture is provided to a tube having an open end and a closedend, wherein the tube and the closed end are closed with respect to thesteam, and the open end is open to allow the steam to move into and outof the tube, wherein a condensed portion of the fluid is allowed to beremoved from the tube by gravitation. In step 602, heat is extractedfrom the tube at the closed end of the tube using a heat sink. In step603, a first portion of the tube is heated up to a specific temperatureusing a heat source that is at a distance from the heat sink and closerto the open end of the tube than the heat sink. In step 604, atemperature of a second portion of the device between the heat sourceand the closed end of the tube or the fluid inside that second portionof the tube, is measured using at least one thermometer. In step 605, itis detected whether a non-condensable gas is present in the tube. Thismay be detected using measurement parameters such as the measuredtemperature and cooling power, or by a detection of condensation at aspecific location inside the tube using visual inspection by e.g. acamera or capacitive detection of condensation.

For example, the heat source is configured to heat the open end of thetube (1) to a temperature in a range from 130 degrees Celsius to 140degrees Celsius, preferably to a temperature in a range from 134 degreesCelsius to 140 degrees Celsius, preferably to a temperature in a rangefrom 135 degrees Celsius to 138 degrees Celsius. For example, thetemperature of the open end of the tube is above the highest temperaturethat occurs in a sterilizer, while not spending excess energy to heatthe device higher than needed.

Fore example, a method of detecting a non-condensable gas in a gasmixture, comprises providing 601 a gas mixture to a tube having an openend and a closed end, wherein the tube and the closed end are closedwith respect to the gas mixture, and the open end is open to allow thegas mixture to move into and out of the tube, wherein a condensedportion of the gas mixture is allowed to be removed from the tube bygravitation; and extracting 602 heat from the tube at the closed end ofthe tube using a heat sink; heating 603 a first portion of the tube upto a specific temperature using a heat source that is at a distance fromthe heat sink towards the open end of the tube; and measuring 604 atemperature of a second portion of the tube between the heat source andthe closed end of the tube or the gas mixture inside that second portionof the tube, using at least one thermometer.

The control unit disclosed herein may comprise one or more processorsand/or software comprising instructions that, when executed by one ormore processors, performs control operations to perform thefunctionality specified in the description. Alternative implementationsof the control unit may also be conceived.

The present invention has been described above with reference to anumber of exemplary embodiments as shown in the drawings. Modificationsand alternative implementations of some parts or elements are possible,and are included in the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

Some or all aspects of the invention, in particular the operations ofthe control unit, may be suitable for being implemented in form ofsoftware, in particular a computer program product. The computer programproduct may comprise a computer program stored on a non-transitorycomputer-readable media. Also, the computer program may be representedby a signal, such as an optic signal or an electro-magnetic signal,carried by a transmission medium such as an optic fiber cable or theair. The computer program may partly or entirely have the form of sourcecode, object code, or pseudo code, suitable for being executed by acomputer system. For example, the code may be executable by one or moreprocessors.

The examples and embodiments described herein serve to illustrate ratherthan limit the invention. The person skilled in the art will be able todesign alternative embodiments without departing from the spirit andscope of the present disclosure, as defined by the appended claims andtheir equivalents. Reference signs placed in parentheses in the claimsshall not be interpreted to limit the scope of the claims. Itemsdescribed as separate entities in the claims or the description may beimplemented as a single hardware or software item combining the featuresof the items described.

References Label Reference [BEN11] Benoit F, Merger D, Hermsen R J, andvan Doornmalen J P C M. A comparison of four commercially availableelectronic steam penetration tests according to ISO 11140 part 4.Central Service, 3: 180-184, 2011. [EN 285] European Committee forStandardization. Standard EN 285: A2: 2009 sterilization - steamsterilizers - large sterilizers, 2015. [EN13060] European Committee forStandardization. Standard EN 13060, Small Steam Sterilizers. Europeanstandard, 2014. [IAWPS] Wagner W, Cooper J R, Dittmann A, Kijima J,Kretzschmar H J, Kruse A, Mares R, Oguchi K, S̆ato H, Stöcker I, SifnerO, Takaishi Y, Tanishita I, and Trűbenbach I J. The IAWPS industrialformulation 1997 for the thermodynamic properties of water and steam.Transactions of the ASME, 122: 150-182, 2000. [ISO11140-4] InternationalOrganization for Standardization. Standard ISO 11140-4 Sterilization ofhealth care products - Chemical indicators - Part 4: Class 2 indicatorsas an alternative to the Bowie and Dick-type test for detection of steampenetration. ISO standard, 2007. [ISO17665] International Organisationfor Standardisation. Standard ISO 17665-1. Sterilization of health careproducts - Moist heat, international organization for standardization,2006. [MIN66] Minkowycz W J and Sparrow E M. Condensation heat transferin the presence of noncondensables, interfacial resistance,superheating, variable properties, and diffusion. International Journalof Heat and Mass Transfer, 9: 1125-1144, 1966. [MRC59] Working party onPressure Steam Sterilizers of the Medical Research Council.Sterilisation by steam under increased pressure. The Lancet, 273:425-435, 1959. [ROS69] Rose J W. Condensation of a vapour in thepresence of a non-condensing gas. International Journal of Heat and MassTransfer, 12: 233-237, 1969. [SYK67] Sykes G. Disinfection &sterilization. 2nd edition with corrections. E & FN Spon Ltd, London,1967. [VDO12-2] van Doornmalen J P C M, Hermsen R J, and Kopinga K. Sixcommercially available class 6 chemical indicators tested against theirstated values. Central Service, 6: 400-404, 2012. [VDO13-2] vanDoornmalen J P C M, Rietmeijer A G M, Feilzer A J, and Kopinga K.Monitoring of steam sterilization processes in the dental office.Central Service, 6: 435-438, 2013. [VDO13-3] van Doornmalen J P C M andKopinga K. Measuring non-condensable gases in steam. Review ofScientific Instruments, 84: 115106, 2013. [VDO14-1] van Doornmalen J P CM, Tessarolo F, and Kopinga K. Measurements of only pressure andtemperature are insufficient to monitor steam sterilization processes: acase study. Central Service, 4: 250-253, 2014. [VDO16-3] van DoornmalenJ P C M Riethoff W. A case study of steam penetration monitoringindicates the necessity of Every Load Monitoring of steam sterilizationprocesses, Central Service 5: 320-324, 2016.

1. A device for detecting a non-condensable gas, comprising a tubehaving an open end and a closed end, wherein the tube and the closed endare closed with respect to a fluid, and the open end is open to allowthe fluid to move into and out of the tube, wherein the tube isconfigured to allow a condensed portion of the fluid to be removed fromthe tube by gravitation; a heat sink configured to extract heat from thetube at the closed end of the tube; a heat source configured to heat afirst portion of the tube up to a specific temperature, wherein the heatsource is located between the open end of the tube and the heat sink;and at least one thermometer configured to measure a temperature of asecond portion of the tube between the heat source and the closed end ofthe tube or the fluid inside that second portion of the tube.
 2. Thedevice of claim 1, wherein the heat source is configured to keep thefirst portion of the tube at a constant temperature.
 3. The device ofclaim 1, further comprising a control unit configured to control theheat source based on a temperature obtained from a thermometerconfigured to measure a temperature of the first portion of the tube. 4.The device of claim 1, comprising a control unit is configured tocontrol the heat sink based on a temperature obtained from the at leastone thermometer in respect of the closed end of the tube.
 5. The deviceof claim 1, wherein the tube is enclosed by a thermally insulatinglayer.
 6. The device of claim 1, further comprising a control unitconfigured to determine information about a composition of the fluidinside the tube, in particular about a presence of any non-condensablegas in the fluid, based on a temperature obtained from the at least onethermometer or a cooling power of the heat sink.
 7. The device of claim1, further comprising a container; wherein the open end of the tube isfluidly connected to an inside of the container via an opening in a wallof the container, and wherein the container is closable to form asubstantially closable chamber that is fluidly connected to a lumen ofthe tube.
 8. The device of claim 7, wherein the heat source isconfigured to heat the open end of the tube to a temperature above atemperature of the inside of the container.
 9. The device according ofclaim 7, wherein the chamber is a sterilizer chamber.
 10. The device ofclaim 7, wherein the container has the opening in a side wall or anupper wall of the container, wherein the chamber is fluidly connected tothe inside of the tube via the opening.
 11. The device of claim 10,wherein the tube is fixed to the side wall or the upper wall of thecontainer, and wherein the tube protrudes from the container in anupward direction.
 12. The device of claim 7, wherein the heat source ispositioned outside the container.
 13. The device of claim 1, wherein adistance between the heat sink and the heat source is at least 5centimeters, preferably at least 10 centimeters.
 14. The device of claim1, wherein a distance between the heat source and the open end of thetube or between the heat source and the wall of the container, measuredalong the tube, is at least 2 centimeters, preferably at least 4centimeters.
 15. A method of detecting a non-condensable gas in a gasmixture, comprising providing a gas mixture to a tube having an open endand a closed end, wherein the tube and the closed end are closed withrespect to the gas mixture, and the open end is open to allow the gasmixture to move into and out of the tube, wherein a condensed portion ofthe gas mixture is allowed to be removed from the tube by gravitation;extracting heat from the tube at the closed end of the tube using a heatsink to cool the closed end of the tube to a temperature below acondensation temperature of a condensable gas in the gas mixture;heating a first portion of the tube up to a specific temperature abovethe condensation temperature of the condensable gas, using a heat sourcethat is at a distance from the heat sink towards the open end of thetube; and measuring a temperature of a second portion of the tubebetween the heat source and the closed end of the tube or the gasmixture inside that second portion of the tube, using at least onethermometer.